Amorphous Carbon Supported Nanoparticles Comprising Oxides of Lanthanides And Method For Preparing Them

ABSTRACT

The invention is directed to bodies comprising an amorphous carbon particle on which are supported nanoparticles of an oxide of lanthanide. These bodies find use as a pharmaceutical for use in a surgery or therapy and diagnostic methods. The bodies can be made by a process comprising impregnating a carbon source material by contacting it with a solution of a salt of said lanthanide; drying said impregnated carbon source material; and subjecting said dried impregnated material to pyrolysis under inert conditions.

The invention is directed to bodies comprising small particles(nanoparticles) of oxides of lanthanides, in particular holmium oxide(Ho₂O₃), which are supported on amorphous carbon particles. Theinvention is further directed to processes for producing these bodies ofcarbon supported nanoparticles, as well as to the use of these bodies ofcarbon supported nanoparticles in therapeutic applications.

Lanthanides, particularly holmium, can be used in radio-embolizationtherapy of liver metastases. Upon neutron irradiation ¹⁶⁵Ho is convertedto ¹⁶⁶Ho which is a beta-radiation emitter. The radio-active holmium hasshown promising results in the radio-ablation treatment of tumors.Intratumoral injections of ¹⁶⁶Ho(NO₃)₃ in a rat model of malignantmelanoma has shown promising results (see Lee, J. D. et al., Eur. J.Nucl. Med. 29(2002)221-230).

Holmium is attractive since it is both a beta- and gamma-emitter whenirradiated to Holmium-166 (¹⁶⁶Ho). Therefore it can be used both innuclear imaging and radio ablation. Moreover, holmium can be visualizedby computed tomography and MRI due to its high attenuation coefficientand paramagnetic properties, as described for instance by Bult, W. etal., Pharmaceut. Res. 26(2009)1371. Poly(L-lactic acid) (PLLA)microspheres are known in the art, which are loaded with holmiumacetylacetonate (HoACAC) (Nijsen, J. F. W. et al., Eur. J. Nucl. Med.26(1999)699-704). The PLLA coating was used to make the HoACACbiocompatible. By administration of these radioactive microspheres intothe hepatic artery, they become trapped in the liver, particularly inand around tumors.

A drawback in the use of the PLLA coating is the sensitivity to neutronradiation, which can result in damage of the coating, see Nijsen, J. F.W. et al., Biomaterials 23(2002)1831-1839.

Also known in the art is the synthesis of ultrafine Gd₂O₃ nanoparticlesinside single-walled carbon nanohorns, as described by Miyawaki, J. etal., Journal of Physical Chemistry B 110(2006)5179-5181. Thedisadvantage of carbon nanohorns is that the methods for producing suchmaterials are difficult to scale up. As a consequence, the cost of usingsuch materials on an industrial level is prohibitively high. Further,Huey-Ing, C. et al., Colloids and Surfaces A: Physiochemical andEngineering Aspects 242(2004)61-69) describes a method for preparingcerium dioxide nanoparticles. However, neither document describes thatthe lanthanide oxide nanoparticles prepared may be supported onamorphous carbon and used in radiotherapy.

An object of the present invention is to provide bodies comprisingnanoparticles of one or more oxides of lanthanides, in particularholmium, which are supported by amorphous carbon. A further object is toprovide these bodies of carbon particles having nanoparticles of oxidesof lanthanides thereon and/or therein, in particular holmium, that maybe used in radiotherapy.

It was found that very small particles comprising oxides of lanthanidescan be made by allowing said oxides to form in combination with carbon.

Thus in a first aspect, the present invention is directed to a bodycomprising an amorphous carbon particle having provided thereonnanoparticles of an oxide of lanthanide. Typically nanoparticles have adiameter of 10 nm or less. The nanoparticles are present on the surfaceof the porous amorphous carbon particle, which surface includes the(inner) pore area.

An amorphous carbon particle, as defined herein, is a carbon materialwithout long-range crystalline order. Short-range order exists, but withdeviations of the interatomic distances and/or interbonding angles withrespect to the graphite lattice as well as the diamond lattice,described by E. Fitzer et al., (IUPAC recommendations 1995) Pure &Applied Chemistry, 67(1995)473-506.

The nanoparticles can be administered when still supported on and/orpresent within the amorphous carbon particles. The bodies of amorphouscarbon particles comprising the supported nanoparticles can be tailoredto any desired size ranging from several tens of nanometers up to onemillimeter or more. Typically their size ranges from 10 μm to 1000 μm,preferably from 15-500 μm, more preferably 20-400, and even morepreferably 25-250 μm. The size of the bodies may be determined by thesize of the starting material. After loading the carbon particles withthe nanoparticles in accordance with the present invention, they may becrushed or milled, optionally followed by size separation (such as bysieving and/or separation based on density differences, e.g. in afluidized bed or so called wind sieving) to obtain bodies of the desiredsize.

The nanoparticles in the body of the present invention preferably have adiameter of 10 nm or less, more preferably the diameter is 5 nm or less.

The bodies of the present invention may be used as a pharmaceutical. Inparticular they may be used for treatment of the human or animal body bysurgery or therapy and diagnostic methods. Such therapy may for instancecomprise radiotherapy, in particular radio-embolization. They can beused for instance in the treatment of liver disorders or kidneydisorders, in particular tumors, more in particular metastases.

The bodies of the invention may be functionalized by attaching one ormore active groups to the surface of the particles. Because the surfacecomprises amorphous carbon, it was found that it is relatively easy toattach chemical groups to the surface. Such active groups may beselected from nucleic acids, lipids, fatty acids, carbohydrates,polypeptides, amino acids, proteins, plasma, antibodies, antigens,liposomes, hormones, markers and combinations thereof.

Another advantage of the bodies of the present invention is that sincecarbon functions as a neutron moderator, the carbon carrier isrelatively stable against neutron irradiation.

The lanthanides series comprises the fifteen metallic chemical elementswith atomic numbers 57 through 71, i.e. the group consisting of La(atomic number 57), Ce (58), Pr (59), Nd (60), Pm (61), Sm (62), Eu(63), Gd (64), Tb (65), Dy (66), Ho (67), Er (68), Tm (69), Yb (70), andLu (71) (lanthanum, cerium, praseodymium, neodymium, promethium,samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium,thulium, ytterbium, and lutetium). Preferably Ho₂O₃ is used as the oxideof lanthanide.

The bodies are in the form of an amorphous carbon particle, which haspores throughout its volume. On the surface of these pores thenanoparticles are dispersed. One of the advantages of the presentinvention is that the dispersion of the nanoparticles is veryhomogeneous.

The diameter of the bodies of the present invention refers to aspherical particle. In case the shape of the bodies deviates fromspherical, the diameter refers to the largest dimension of the particle.Preferably the bodies of the present invention are spherical oressentially spherical, in particular having a sphericity of close to 1,for instance more than 0.75, preferably more than 0.85. The sphericityof a certain particle is the ratio of the surface area of a spherehaving the same volume as said particle to the surface area of saidparticle.

Also the nanoparticles of crystalline oxide of lanthanide are typicallyessentially spherical, viz. having a sphericity of more than 0.85,preferably about 1.

Although the lanthanide oxide particles in the bodies of the presentinvention are very small, the crystal structure is the same as thenormally occurring crystal structure of the bulk oxide material, whichis cubic for all oxides of lanthanides.

A homogeneous distribution of the lanthanide oxide precursor isimportant to produce small metal oxide particles homogeneouslydistributed throughout the obtained bodies. For this reason the carbonprecursor material is contacted, in particular impregnated, with asolution of a salt of the corresponding lanthanide. Aqueous solutionsare preferred. Preferably the corresponding lanthanide nitrate is used,because these generally have a good solubility in water. Thecorresponding Cl⁻, Br⁻ and I⁻ salts could also be used but these areless preferred, since they may give rise to the formation of thecorresponding halogen compounds, which is undesired.

The bodies of the present invention may be produced by a processcomprising the steps of:

-   -   impregnating a carbon source material by contacting it with a        aqueous solution of a salt of said lanthanide;    -   drying said impregnated carbon source material; and    -   subjecting said dried impregnated material to pyrolysis under        inert conditions.

The size of the nanoparticles comprising the crystalline lanthanideoxide on the bodies of the present invention can be controlled bychoosing the concentration of lanthanide salt in the aqueous solution. Ahigher concentration leads to nanoparticles having a larger diameter anda lower concentration to smaller nanoparticles. Typical concentrationsare in the range of 0.01-1.5 g/ml, preferably 0.1-1 g/ml, depending onthe solubility of the salt.

The carbon source material is a material that contains sufficient carbonatoms to produce essentially carbon containing particles upon pyrolysis.Suitable materials are for instance cellulose, preferablymicrocrystalline cellulose (MCC, which is for instance described inWO-A-2007/131795, incorporated herein), but also other materials, suchas cotton may be used; carbohydrates, such as sugar or chitosan; andactive carbon. Very suitable MCC particles are obtainable under thetrade name Cellets™, which are available in a broad range of diameters,for instance from 100-200 μm to 1000-1400 μm and which have a sphericityof 0.9 to 0.95.

Typically the drying step is carried out until the dried product reachesconstant weight. Preferably the drying is carried out at roomtemperature (about 25° C.).

The pyrolysis step is carried out by heating the dried impregnatedmaterial to a temperature that is sufficient to convert most or allnon-carbon material into volatile compounds. This step is carried outunder inert conditions, viz. under conditions that avoid reaction ofcarbon with the surroundings. Preferably these conditions compriseexclusion of oxygen from air. This may preferably be obtained bycarrying out the pyrolysis under a typical “inert” gas, such as nitrogenor a noble gas, such as argon or helium, which is used to dissipate theoxygen containing air.

Typically the carbon particles shrink upon pyrolysis, resulting in thebodies of the present invention, for instance by 10-30%, relative totheir original diameter.

The process of the present invention may also include a following stepwherein the amorphous carbon particle is removed, thereby obtainingnanoparticles in a pure form. Typically the amorphous carbon particlemay be removed by oxidation to carbon dioxide. Oxidation with gaseousoxygen can be done by thermal treatment in an oxygen-containing gas flowat a temperature below about 500° C.

FIG. 1 shows a Transmission Electron Micrograph (TEM) image of a crushedbody in accordance with the present invention comprising amorphouscarbon particles on which the nanoparticles are supported.

FIG. 2 shows a high resolution TEM (HR-TEM) image of carbon supportedholmium oxide particles of the present invention. Lattice fringes areexhibited. The dashed circle in this figure shows a nanoparticle havinga diameter of approximately 5 nm.

FIG. 3 shows a TEM-image (high angle annular dark field, HAADF) ofcarbon supported holmium oxide particles of the present invention.

FIG. 4 shows an elemental analysis along the arrow indicated in FIG. 3.The oxygen signal points to holmium oxide nanoparticles.

FIG. 5 shows a Scanning Electron Micrograph (SEM) picture of bodies ofcarbon supported holmium oxide particles of the present invention at lowmagnification, produced according to the following example.

FIG. 6 shows schematically a body (1) according to the present inventioncomprising a porous amorphous carbon carrier particle (3) on which arepresent nanoparticles (2) of an oxide of lanthanide.

The invention will now be illustrated by the following non-limitingexample.

EXAMPLE

2 grams of hydrophilic MCC spheres (Cellets™ 100 obtained fromSynthapharm, particle size distribution of 100-200 μm) were loaded viawet impregnation. To this end the spheres were immersed in an aqueoussolution of holmium nitrate pentahydrate (2 g Ho(NO₃)₃.5H₂O,Sigma-Aldrich, 99.9% purity, in 20 ml H₂O). The spheres were left for 24h within the solution with occasional stirring. Next, the impregnatedspheres were filtered using a Buchner funnel with glass filter, afterwhich the isolated spheres were dried at 80° C. to constant weight atroom temperature. Subsequently pyrolysis was performed at 800° C. undera stagnant nitrogen atmosphere for 3 h. Scanning- and transmissionelectron microscopy were employed to image the resulting holmiumparticles and the carbonaceous support. Conventional TEM, as well aselectron diffraction patterns were recorded.

From the TEM-image of FIG. 1 and the HR-TEM image of FIG. 2 it isdeduced that particles of a very small crystallite size (below 5 nm) areformed supported within an amorphous carbon. The STEM-image with HAADFdetector (FIG. 3) shows the same. Elemental analysis (FIG. 4) shows thatoxygen is abundant in the sample which suggests that holmium is presentin an oxidic state. Electron diffraction (not shown) substantiates thatholmium is present as Ho₂O₃ in a cubic crystal structure. FIG. 5 showsthe bodies of the invention on a low magnification, indicating that theimpregnated MCC particles have a homogeneous size distribution afterpyrolysis.

1. A process for producing bodies comprising nanoparticles of an oxideof lanthanide supported on amorphous carbon particles, which processcomprises impregnating a carbon source material by contacting it with asolution of a lanthanide salt; drying said impregnated carbon sourcematerial; and subjecting said dried impregnated material to pyrolysisunder inert conditions.
 2. The process according to claim 1, furthercomprising removing the amorphous carbon particles, whereby thenanoparticles are obtained in pure form.
 3. The process according toclaim 2, wherein the amorphous carbon particles are removed by thermaltreatment in an oxygen-containing gas flow at a temperature below about500° C.
 4. The process according to claim 1, wherein the bodies have adiameter of 10-1000 micrometers.
 5. The process according to claim 1,wherein the oxide of lanthanide nanoparticles have a diameter of 10 nmor less.
 6. The process according to claim 1, wherein the oxide oflanthanide nanoparticles have a diameter of 5 nm or less.
 7. The processaccording to claim 1, wherein the oxide of lanthanide is holmium oxide.8. The process according to claim 1, wherein the oxide of lanthanide isHo₂O₃.
 9. The process according to claim 1, wherein the bodies aresubstantially spherical.
 10. The process according to claim 1, whereinthe bodies have a diameter of 15-500 μm.
 11. The process according toclaim 1, wherein the bodies have a diameter of 20-400 μm.
 12. Theprocess according to claim 1, wherein the bodies have a diameter of25-250 μm.
 13. The process according to claim 1, comprising impregnatinga carbon source material by contacting it with an aqueous solution of alanthanide salt, the solution having a lanthanide salt concentration offrom 0.01 to 1.5 g/mL.
 14. The process according to claim 13, whereinthe concentration is from 0.1 to 1 g/mL.
 15. The process according toclaim 1, wherein the salt is a lanthanide nitrate.
 16. The processaccording to claim 1, wherein the salt is holmium nitrate.